Glaucoma is a chronic disease where progressive irreversible damage to the optic nerve results in gradual permanent loss of the peripheral vision. Glaucoma is often associated with elevated pressure within the eye (intraocular pressure/IOP).
The eye normally maintains a stable IOP by balancing the production of fluid with the outflow of fluid into the drainage pathway. In general “normal” eye pressure ranges between 12 and 21mmHg. Patients with glaucoma often have eye pressures higher than the normal range without treatment.
Open Angle Glaucoma
In open angle glaucoma (OAG) the drainage pathway, or ‘angle’ of the eye, is open or unobstructed.
Patients with OAG usually have no symptoms until the glaucoma is advanced and they require a thorough eye exam to have the disease identified and treated.
Primary open angle glaucoma (POAG) is the most common type of glaucoma and is idiopathic, meaning we do not understand the cause. Common associations or risk factors for POAG are age and genetics (runs in the family). Certain ethnic populations have higher rates of POAG including African American, Latino, Caribbean and others.
Normal Tension Glaucoma (NTG) is a form of open angle glaucoma where the optic nerve is damaged despite eye pressures remaining in the normal range. Patients with NTG are more likely to have a systemic condition that contributes to their glaucoma progression. Common systemic associations with NTG including:
- Nocturnal hypotension: Nighttime blood pressure is too low resulting in insufficient blood supply to the optic nerve. Diastolic blood pressure under 60mmHg is usually considered too low.
- Sleep apnea: Patients may hold their breath for periods while they sleep, which temporarily causes an increase in IOP resulting in optic nerve damage.
- Anemia/blood loss: Insufficient oxygenation of optic nerve leads to damage because of low blood oxygen levels.
Closed Angle Glaucoma
In Closed Angle Glaucoma (CAG) the drainage pathway in the anterior chamber ‘angle’ can close either suddenly (acute), intermittently, or chronically, causing the IOP to build in the eye. CAG is a less common type of glaucoma but often is more severe and can lead to blindness if not identified early and treated.
Patients with acute CAG can develop sudden very high IOP that causes eye pain and redness, severe headache above the brow, haloes around lights, blurry vision, nausea and vomiting. Acute CAG is a medical emergency and without treatment with medications and lasers patients are at risk of rapid permanent blindness. Patients with intermittent or chronic CAG may not have any visual symptoms and require an eye exam to have their glaucoma disease identified.
Primary CAG is often related to an anatomical predisposition where the front segment of the eye is naturally smaller and more crowded. It can be associated with far-sightedness (hyperopia), cataracts, and is more common in South Asian and Inuit populations. Patients with narrow ’angles’ at risk of CAG can be identified with an eye examination and treated with a preventative laser (laser peripheral iridotomy). Less commonly, patients can have an abnormal iris shape called plateau iris syndrome that results in narrowing of the angle.
Secondary CAG is rare and usually results from abnormal blood vessels (neovascularization) growing over the drainage pathway angle. Neovascular glaucoma is usually caused by severe retinal damage from diabetic retinopathy, a blockage in a retinal vein (RVO) or artery (CRAO), or radiation retinopathy. Neovascular glaucoma is a severe problem that can be challenging to treat successfully and often results in blindness.
What are the symptoms of glaucoma?
The vast majority of patients with glaucoma do not have any visual symptoms. If left untreated, glaucoma can cause irreversible and permanent loss of the peripheral field of vision that eventually encroaches on the central vision. Despite this, patients rarely notice a change in peripheral vision until the disease is advanced.
Rarely, if the IOP increases significantly as in acute CAG, patients may develop eye pain and redness, severe headache above the brow, haloes around lights, blurry vision, nausea and vomiting. Acute CAG is a medical emergency and without treatment patients are at risk of permanent blindness.
How is glaucoma diagnosed?
A glaucoma diagnosis is based on one or a series of comprehensive eye examinations with IOP measurement and with specialized testing including visual fields to assess the peripheral vision and optic nerve imaging using optical coherence tomography (OCT). Glaucoma can be diagnosed by an optometrist or an ophthalmologist.
Can glaucoma be cured?
Glaucoma is a chronic eye disease that can be managed but not cured. Any peripheral visual field damage from glaucoma is irreversible. Treatment is initiated to halt or reduce disease progression.
How is glaucoma treated?
Glaucoma is usually treated by lowering the eye pressure in the eye. This can be done with daily prescription eye drops, laser trabeculosplasty (SLT), and/or glaucoma surgery. Your eye doctor will discuss with you the treatment options for your type of glaucoma.
Patients with NTG should be assessed by a family doctor or internist to ensure that sleep apnea, nocturnal hypotension and anemia risks are identified and treated if necessary.
All patients with glaucoma require ongoing monitoring through comprehensive eye examinations with IOP measurements and specialized testing.